Correlations between 21 cm Radiation and the CMB from Active Sources

TL;DR

This paper investigates how active sources like cosmic strings could produce observable correlations between 21 cm radiation and the CMB, providing a potential new probe of physics beyond standard models.

Contribution

It introduces a calculation of the expected correlations induced by cosmic strings between 21 cm signals and the CMB, highlighting their potential observability as evidence for new physics.

Findings

Cosmic strings can generate detectable correlations between 21 cm and CMB anisotropies.

Passive inflationary perturbations predict no such cross correlations before reionization.

Observation of these correlations would indicate active sources like cosmic strings.

Abstract

Neutral hydrogen is ubiquitous, absorbing and emitting 21 cm radiation throughout much of the Universe's history. Active sources of perturbations, such as cosmic strings, would generate simultaneous perturbations in the distribution of neutral hydrogen and in the Cosmic Microwave Background (CMB) radiation from recombination. Moving strings would create wakes leading to 21 cm brightness fluctuations, while also perturbing CMB light via the Gott-Kaiser-Stebbins effect. This would lead to spatial correlations between the 21 cm and CMB anisotropies. Passive sources, like inflationary perturbations, predict no cross correlations prior to the onset of reionization. Thus, observation of any cross correlation between CMB and 21 cm radiation from dark ages would constitute evidence for new physics. We calculate the cosmic string induced correlations between CMB and 21 cm and evaluate their observability.